mercury in various biological products (for example, influenza virus vaccine and immune serum globulin) resulting from the use of mercurial preservatives, (2) develop methodology for the quantitative analysis of the thimerosal molecule and any of its degradation products, (3) determine stability of mercury and thimerosal in various products, and (4) determine different mercury species present in various products containing thimerosal such as Immune Serum Globulin, DTP Vaccine, etc. Cold vapor atomic absorption spectrophotometric methodology has been developed to determine the total mercury resulting from mercurial preservatives such as thimerosal, phenylmercuric nitrate and phenylmercuric borate in various injectable biological products. Validation studies for total mercury have been completed for each of the major product types. The cold vapor atomic absorption spectrophotometric procedure used with this sample digestion procedure yields highly accurate and precise results for total mercury in these samples matrices. Thimerosal stability studies are being conducted with a number of different biological products. Thimerosal has been separated from one of its degradation products, thiosalicyclic acid, by two reverse phase liquid chromatographic procedures. Liquid chromatography with an amperometric detector polarography or gas chromatography/mass spectrometry will be explored as methods for the quantitative and/or structural characterization of the thimerosal and its degradation products. Liquid chromatography combined with inductively coupled argon plasma emission spectrometry/mass spectrometry (LC-ICP/MS) has been used to quantitate thimerosal in diluent, a Tetanus Toxoid Adsorbed and an Influenza Virus Vaccine. Work is being done on immune serum globulin by this technique. Methods are being developed to detect mercury in vaccines in which mercury has been minimized to meet current safety standards for the use of thimerosal in childhood vaccines. Instrumentation is being developed to lower the detection limit of the method.